diff --git a/httplib.h b/httplib.h
index 1c98cc80bc..3cd371cbee 100644
--- a/httplib.h
+++ b/httplib.h
@@ -5568,6 +5568,15 @@ inline bool mmap::open(const char *path) {
     is_open_empty_file = true;
     return false;
   }
+
+  // A failed mapping must not be left in `addr_`: `is_open()` only compares it
+  // against nullptr, so the MAP_FAILED sentinel would pass and `data()` would
+  // hand the caller (const char *)-1.
+  if (addr_ == MAP_FAILED) {
+    addr_ = nullptr;
+    close();
+    return false;
+  }
 #endif
 
   return true;
diff --git a/test/test.cc b/test/test.cc
index b71171f75d..04e130a18a 100644
--- a/test/test.cc
+++ b/test/test.cc
@@ -9163,6 +9163,23 @@ TEST(MmapTest, OpenWhileFileHeldForWriting) {
 }
 #endif
 
+#ifndef _WIN32
+// A failed ::mmap must not be reported as an open mapping. is_open() only
+// compares addr_ against nullptr, so the MAP_FAILED sentinel used to pass it
+// and data() handed the caller (const char *)-1. A directory opens and stats
+// fine but has no mapping, so ::mmap fails for it.
+TEST(MmapTest, FailedMappingIsNotOpen) {
+  const char *path = "./mmap_failed_mapping_test_dir";
+  ASSERT_EQ(0, ::mkdir(path, 0755));
+  auto dir_cleanup = detail::scope_exit([&] { ::rmdir(path); });
+
+  detail::mmap m(path);
+  EXPECT_FALSE(m.is_open());
+  EXPECT_NE(static_cast<const void *>(m.data()),
+            static_cast<const void *>(MAP_FAILED));
+}
+#endif
+
 TEST(KeepAliveTest, ReadTimeout) {
   Server svr;